Description
CPSC 250L Lab 4
1 Introduction
The focus for this lab is file input and output as well as string formatting. Check the JavaDoc
for File, Scanner, PrintWriter, and String.format.
2 Exercises
2.1 Line Numbers
In this exercise, you will read in a file, prepend line numbers to each line, and then output
it to another file.
Exercise 1
Create a class named LineNumbers and implement the following method in it.
• public static void process(File input, File output)
This method receives a text file. The method writes all lines from the input file to the
output file with each line preceded by its line number formatted as follows:
| Original Line
The line number should be right aligned in three spaces, be followed by a space, then
a pipe, another space, and lastly the original line. For example:
Input File:
This is a line of text
Yet another line
You only live twice
.
.
.
This is the last line
Output File:
1 | This is a line of text
2 | Yet another line
3 | You only live twice
.
.
.
123 | This is the last line
Test your code against LineNumbersTest.java. When all tests pass proceed to the next
exercise.
Exercise 1 Complete
Run:
git add .
git commit -m “Completed exercise 1”
git push origin master
2.2 Cookie Jar
Exercise 2
Create a class named CookieJar and implement the following method in it.
• public static void cashingIn(File input, File output)
This method receives an input file with your count of coins given as pairs of integer and
type of coin, e.g., 1 penny, 42 quarters, 9 nickels. The method reads number/cointype pairs from the input file and write the total dollar amount to the output file.
For
example, given the input file 2 quarters 4 dimes 1 penny 3 nickels 3 pennies,
the method prints You have $1.09 in the jar to the output file. The dollar amount
should be formatted in 2 decimal places and with commas (when appropriate). In cases
when the total amount in the jar is zero the method writes
Code:
You have no money in the jar
to the output file. The input file may contain coin pairs in one line or across different
lines, may contain several counts of the same type of coin at different times, and may
list the type of coin in plural or singular form, e.g., pennies for many 1 cent coins
or penny for one coin. Pennies are worth 1 cent each, nickels are worth 5 cents each,
dimes are worth 10 cents each, and quarters are worth 25 cents each.
Test your code against CookieJarTest.java. When all tests pass, proceed to the next
exercise.
Exercise 2 Complete
Run:
git add .
git commit -m “Completed exercise 2”
git push origin master
2.3 Album and Comparable
In this exercise, we implement a Comparable type called Album.
Exercise 3
Open the Album class provided in the Git repository and implement the following methods.
1. public Album(String _name, String _author, int _length)
This constructor receives two Strings representing the album name and band name
respectively, as well as an int which represents the Album’s runtime in seconds. You
should set the fields in Album to these values.
2. public int compareTo(Album other)
This method receives another Album object and returns a negative value if this Album
is less than other, 0 if the Albums are the same, and a positive value if this Album is
greater than other. The comparison is described as follows.
(a) If author does not equal other.author, return the lexicographical comparison of
author and other.author.
(b) Else if name does not equal other.name, return the lexicographical comparison of
name and other.name.
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(c) Otherwise, return the difference between length and other.length.
3. public String getName()
This method returns the Album’s name.
4. public String getAuthor()
This method returns the Album’s author.
5. public int getLength()
This method returns the Album’s length.
Test your code against AlbumTest.java.
Exercise 3 Complete
Run:
git add .
git commit -m “Completed exercise 3”
git push origin master
2.4 Discography
For this exercise, we will read a list of Albums from a file, sort them, and then output the
sorted list to another file.
Exercise 4
Your local library has compiled a list of all CD albums available in their collection. The
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information is written in a comma-separated value (CSV) text file, where each line has
the name of an album, its author and the length of every song in that album (in minutes
and seconds). For example, the entry for the CD “Best of Elmo” is “Best of Elmo,Sesame
Street,2:29,1:30,2:09,1:46,1:55,2:02,1:42,2:40,
1:56,1:30,2:03,1:14,2:28,2:47”.
Given an input text file with a group of CD data (each album in one line) the library wants
all albums sorted and formatted for easy reading.
The output is formatted as follows.
• The first column lists authors, which are left aligned in as many spaces as the length
of the longest author in the input file. Authors are sorted alphabetically.
• The second column lists album names, which are left aligned in as many spaces as the
longest album name in the input file. Albums from the same author will be sorted
alphabetically by name.
• The third column list the total running time of albums, which are in the form H:MM:SS,
where H is hours (0-9), minutes (0-59), and seconds (0-59). Minutes and seconds are
displayed in 2 spaces (with a leading zero if needed).
Each column is divided by a | character (with a space before and after).
For example input and output look at the sample-discography-input1.txt and
sample-discography-output1.txt included with the Git repository.
Create a Discography class and implement the following method.
• public static void writeReport(File input, File output)
This method should read in each Album from the input files into an ArrayList of Album
objects. You should then use Collections.sort to sort your ArrayList. Then output
each album’s information to the output file using the above formatting guidelines.
Hint: If you want, you can implement a toString() in Album that returns the Album’s
data in the expected format.
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Test your code against DiscographyTest.java.
Exercise 4 Complete
Run:
git add .
git commit -m “Completed exercise 4”
git push origin master
3 Common Mistakes
The following are warnings about and solutions to common mistakes for this lab.
1. Be sure to close your Scanners and PrintWriters!
2. When iterating through a File’s contents, ensure that you do not go past the end of
the file.
3. Pay close attention to the format of your output.
4. Ensure that you handle any exceptions that your code may throw.
5. In the Discography exercise, use the Album class!
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CPSC 250L Lab 4
